Photo-electric tube



Aug. 9, 1932. P. H. BRACE PHOTO-ELECTRIC TUBE Original Filed June 30,1921 WITNESSES: JGZZM ATTORNEY Patented Aug. 9, 1932 I UNITED STATESPATENT- OFFICE PORTER H. BRAGE, 0F WILKINSBURG, PENNSYLVANIA, ASSIGNORTO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OFPENNSYLVANIA PHOTO-ELECTRIC TUBE Application filed June 30, 1921, SerialNo. 481,469. 'Renewed December 18, 1929.

My invention relates to electron tubes or audions and particularly tothose electron tubes in which it is not necessary to heat the cathode inorder to cause electrons to be emitted therefrom.

One object of my invention is to provide an electron tube which, becauseof its special construction and arrangement of parts,

shall be very sensitive in its operation and which shall be particularlyadapted for use as a sensitive detector having a minimum distortingefiect.

Another object of my invention is to obviate the disadvantages of theordinary thermionic tube by employing a cold cathode and utilizing whathas come to be known in the art as the photo-electric effect or theproperty of certain bodies of giving off electrons when exposed tolight.

A further object of my invention is to the tube electrodes as ispossible with a cold cathode. It also prevents the location of thecontrol electrode in as close proximity to I the cathode as isdesirable.

Furthermore, because of the resistance of the filament, there will be adifi'erence of potential between the two ends thereof, or, in otherwords, a otential gradient will exist over the remain er of the filamentwith respect to one end. Hence, it is impossible for all parts of thefilament to be at the same potential with respect to the controlelectrode or grid, a condition which reduces the capacity andsensitiveness and, at least for certain uses, impairs the efliciency ofthe tube. a

In my electron tube I utilize the photo electric effect to produce theemission of electrons from the cathode and by this means,

together withthe novel form of cathode and the relative arrangement ofthe electrodes hereinafter described in detail, I overcome the abovementioned difficulties. It is well knownthat certain substances emitelectrons when exposed to light. Examples of such substances are thealkali metals, for instance, potassium. In order to make use of thephoto-electric effect in' an electron tube, I employ as the cathode analkali metal such as potassium and I so arrange a source of light thatits rays shall fall upon the hotoelectrically active surface of thecatho e. A source of light of short wave-length is preferable.

The usual anode and control electrode are provided. In the preferredembodiment of my invention, the cathode is made cylindrical in form, andthe control electrode, the anode and the light source are all disposedwithin the cylindrical cathode so that the cathode surrounds all of theother elements of the tube.

In the drawings, Figure 1 is a longitudinal .sectional view of myelectron tube.

Flg. 2 1s a transverse sectional view taken .stance 4, for example,potassium. The photoelectrically sensitive coat 4 constitutes thecathode. The envelope 3 may be exhausted or may be filled with asuitable gas at certain low pressures, for example, helium, at a pres-,

sure of a few millimeters of mercury. Making electrical connection tothe cathode 4, is a terminal 5. I i

A helix or other reticulated cylinder 6 of metallic wire or gauzeconstitutes the control electrode or grid, which is completelysurrounded by the cathode 4. A similar helix or other reticulatedcylinder 7 of metallic wire or gauze, lying within the control electrode6, constitutes the anode of the tube. Terminals 8 and 9 are provided forforming electri cal connection with the grid 6 and the anode 7respectively.

The operation of my electron tube is as follows. When the discharge tube1 is energized, the rays of li ht therefrom pass through the meshes of te cylinders 7 and 6 and strike the surface 4 of the cylindrical 10'cathode, thereby causing it to emit electrons.

The electrons travel in the direction of the anode 7, and the number ofelectrons reaching the anode may be controlled exactly as are theelectrons from the heated filament in the 10 ordinary audion tube, thatis, by the variation of the relative potentials of the anode 7, grid 6and cathode 4.

Since all portions of the surface of the oathode 4 are at the samepotential, there is no potcntial gradient over it with respect to the.

control electrode and, therefore, the electron emission from thecathodewill be a maximum for any given set of relative potentials between thecathode, control electrode and anode.

Because the light comes from a distributed source, there will be noshadows cast upon the surface of the cathode by the anode and controlelectrode, consequently, the emission of a0 electrons over the entirearea of the cathode will be uniform.

It will be seen that, by reason of the novel configuration of thecathode and the arrangement of the grid and anode so that they are bothsurrounded by the cathode, a much larger proportion of the totalelectrons emitted by the cathode will reach the anode than in a tube ofthe ordinary filament type. This construction, combined with theunipotential cathode and the positioning of the control electrode inclose proximity to the cathode, enables me to produce an electron tubethat is more sensitive than those which have been made heretofore.

Though I have shown a preferred construction illustrating the principlesof my invention, it will be understood that various modi- 'ficationswill suggest themselves to those skilled in the art. I desire,therefore, that my invention shall be limited solely by the prior artand the scope of the appended claim.

By the term line-source of light, as used in certain'of the-claims, ismeant simply a source which possesses considerable length relative toits breadth.

I claim as my invention:

An electron-tube device comprisinga discharge lamp as a source of light,an apertured tubular anode surrounding said lamp and spaced therefrom,an apertured tubular control electrode surrounding said anode and lampand spaced therefrom, and a tubular cathode, said cathodeconstitutingthe outermost electrode and having its inner surface 6 madeof a material which emits electrons in response to light rays thespacing of said anode and said control electrode from said lamp beingsufiicient to prevent shadows being cast thereby on said cathode whensaid lamp is in operation.

In testimony whereof, I have hereunto subscribed my name this 23rd dayof June, 1921.

PORTER H. BRAOE.

